1. Field of the Invention
This invention relates to sound insulation and to the attachment of an insulating layer to a sheet material, for example, dash mats for automobiles.
2. Description of the Related Art
In most contemporary automobiles, a steel fire wall separates the engine compartment from the passenger compartment. To reduce the transmission of sound from the engine compartment through the fire wall and into the passenger compartment, a sound barrier mat (otherwise known as a dash mat) is typically constructed of an elastomeric material and is mounted to and substantially overlies the fire wall. An absorber layer, typically constructed of an open cell foam material, is attached to the sound barrier mat and interfaces between the sound barrier mat and the firewall. An outer surface of the sound barrier mat is typically in contact with a bottom surface of the vehicle carpet and extends beyond the carpet to an upper portion of the fire wall behind the instrument panel. It is common to attach the absorber material to the sound barrier mat through the application of hot melt glue or spray adhesive. Adhesives that are capable of bonding the foam material to the elastomeric mat are dissolved in solvents which are typically ozone depleting and must be handled with extreme care. Many of these types of adhesives are no longer being manufactured due to environmental concerns and new industrial standards. A technique known as heat staking has been used as an alternative to ozone-depleting adhesives. However, the layers must be properly aligned and temporarily fastened together before heat staking. It would be advantageous to attach the absorber layer to the sound insulating layer without the difficulties encountered with adhesives or temporary fasteners.